This invention relates generally to railway vehicles and in particular to the improved steering of railway vehicles around curves.
In a conventional railway vehicle truck or "bogie", wheel set assemblies are restrained longitudinally and laterally by contact with rub plates on the truck frame to travel in nearly the same direction as the frame. On straight track the directional restraint of the wheel set assemblies is acceptable. However, on curving track it would be desirable for the leading wheel set assembly to angle in the direction of the curve, and the trailing wheel set assembly to angle opposite to the leading wheel set assembly. In this manner the truck would be "steered" around a curve.
These differences between preferred and actual wheel set angles are sufficient to develop lateral creep forces at the wheels which are limited only by wheel-rail friction. Such friction not only results in high levels of wear on both rails and wheels, but it is also a significant contributing factor to derailment by tipping the rail over. Reduction of these lateral forces is the primary object of this invention.
Although this problem is not confined to a particular type of railroad vehicle, it is however, particularly severe with large, 3-axle locomotive trucks since the difference between the preferred angle of travel of the leading and trailing wheel set assemblies is proportional to the truck length. The problem is further aggravated in that the tractive force of a locomotive exerted on an associated wheel set assembly pushes it against the truck frame, thereby further restraining the wheel set direction of travel to that of the frame. Furthermore, the wheel-rail friction of a locomotive is relatively large due in part to its characteristically heavy wheel loadings, and the resulting combination of this, together with the above-described strong lateral forces developed by the locomotive wheel set angular differences in a curve, can generate an increase in detrimental friction related affects such as noted hereinabove.
Accordingly, a certain amount of wheel set assembly angling is desirable while traversing curves to improve railway vehicle truck performance. However, a degradation of truck performance can result from insufficiently restrained wheel set assemblies as exemplified by the phenomenon of truck hunting defined herein as an oscillatory motion consisting of combined yawing and lateral displacement of the truck. Accordingly, it is another object of the present invention to avoid this type of performance degradation in a self-steered railway vehicle truck.
Prior self-steering truck designs as exemplified by U.S. Pat. No. 4,136,620 to Scheffel et al and U.S. Pat. No. 4,164,188 to Hallam et al have typically employed mechanically interconnected wheel sets. Such designs require a substantial amount of undercarriage space and are not easily adaptable to existing truck designs. Accordingly, it is still another object of the present invention to provide a new and improved self-steering railway vehicle truck which can be relatively easily employed in existing truck designs or retrofitted into existing trucks.